Shoe retracting system for internal shoe drum brakes, and brakes including same

ABSTRACT

A drum brake is disclosed which includes a lever pivotally attached to one of the shoes. The lever has a hooked end which is attached to one end of a return spring which is stretched between the shoes. A cam member is rotatably mounted on the one shoe and includes an eccentric mounted thereon which engages a slot in the lever. Rotation of the cam member moves the lever from a first position in which the return spring is relaxed to a second position in which the spring is stressed to exert a force on the shoes. The cam member is accessible from the exterior of the brake so that an appropriate tool may be used to rotate the cam member.

United States Patent [72] Inventor Bernard Laverdant 2,621,761 12/1952 Smith 188/79.5(SS) Vincennes, France 3,203,512 8/ 1965 Lepelletier l88/216X [g l fiP- 1 3 5 FOREIGN PATENTS 21 i e an. Patented Mar. 1971 555,581 8/1943 Great Britain 188/216 [73] Assignee Societe Anonyme D,B.A. Primary Examiner-Duane A. Reger Pari Fran AttorneysCecil F. Arens and Plante, Arens, Hartz, Hix and [32] Priority Jan. 26, 1968 Smith [33] France 137,591

[54] SHOE RETRACTING SYSTEM FOR INTERNAL SHOE DRUM BRAKES, AND BRAKES INCLUDING SAME 4 Claims, 2 Drawing Figs.

[52] US. Cl 188/216, 188/79.5 [51] Int.Cl Fl6d 65/58 [50] Field of Search 188/795 (GT). 55, 216

[56] References Cited UNITED STATES PATENTS 1,663,295 3/1928 Dodge 188/216 ABSTRACT: A drum brake is disclosed which includes a lever pivotally attached to one of the shoes. The lever has a hooked end whichis attached to one end of a return spring which is stretched between the shoes. A cam member is rotatably mounted on the one shoe and includes an eccentric mounted thereon which engages a slot in the lever. Rotation of the cam member moves the lever from a first position in which the return spring is relaxed to a second position in which the spring is stressed to exert a force on the shoes. The cam member is accessible from the exterior of the brake so that an appropriate tool may be used to rotate the cam member.

Fatehtdf 30, i ii $1195 RETRAQTING SYSTEM FOR INTERNAL SHOE DRUM BRAKES, AND BRAKES TNCLUDTNG SAME The present invention relates to a shoe retracting system for internal shoe drum brakes and it has for its principal object to provide means for easily hooking the usual shoe return spring or springs upon brake mounting and unhooking same upon brake dismounting. It is of a particular interest whenever the brake shoe webs display poor accessibility once the shoes are located in their operating position, as may be experienced with some kinds of internal shoe drum brakes comprising a double backing plate, which usually hinders the hooking of one or more prestressed springs on said brake shoes.

A more general object of the invention is to provide an internal shoe drum brake including a shoe retracting system according to the principles which will be set forth hereinafter.

According to a feature of the invention, there is provided, between one end of the usual return spring or springs and the brake shoe on which it is to be hooked, a lever member pivotally connected at one end thereof to the brake shoe web and formed at its opposite end with a hook portion, this lever member being disposed generally transversely to the spring axis and being adapted to be pivoted by an associated positioning means between two distinct angular positions corresponding respectively to the stressed and to the unstressed condition of said return spring or springs.

According to another feature of the invention, the associated positioning means, which is operable from the outside of the brake, consists of a rotating cam member carried by the brake shoe web and provided with an eccentric member which is slidably received in a slot or similar opening of the lever member so as to cause the latter to pivot from one of said angular positions to the other as said cam member is rotated about its axis by means of an appropriate tool. By engaging the bottom portion of said slot, the eccentric member preferably determines at least one of said angular positions of the pivoting lever member, particularly that one which corresponds to the stressed condition of the associated ,retum spring; and, advantageously, this last-mentioned angular position will be reached for a displacement of the rotating cam member beyond that corresponding to the greatest elongation of the spring, thereby providing for a self-locking of the pivoting lever member in its operative position.

The features and advantages of the present invention will be best understood from the following description of a preferred embodiment, given by way of example only and with reference to the accompanying drawings, in which:

FIG. l is a simplified elevational view showing the shoes of an internal shoe drum brake and an associated shoe retracting system in accordance with the principles of this invention; and

F 16. 2 is an enlarged scale view of the pivoting lever member and associated positioning means in both angular positions corresponding respectively to the stressed condition (in solid lines) and to the unstressed condition (in dotted lines) of the associated return spring.

Referring first to FiG. 1, there is shown a pair of brake shoes 10,12 disposed in a known end-to-end relationship inside an internal shoe drum brake (not shown). These brake shoes are normally urged toward each other in a retracted position and held in abutting engagement with anchoring means or interconnecting struts (not shown) by one or more return springs 14 which are stretched therebetween. It will be observed that, whereas one end of the spring 14 is directly attached to the web of brake shoe 12, its other end is hooked on shoe 10 through the intermediary of a pivoting lever 16 shown in more detail on the view of FIG. 2. The lever 16 is pivotally connected at its lower end to the web of brake shoe 10 through a pivot pin 18 and terminates at its upper end with a hook portion adapted to be engaged by the end of spring 14. lntermediate its ends, the lever is formed with an open slot 20 limited by a pair of parallel edges extending substantially radially with respect to pivot pin 18, and by a rounded interconnecting bottom portion; alternatively, the slot 20 could be closed at both ends without departing from the spirit of the invention. Between the edges of slot 20 is slidably received an eccentric pin 22 secured to a rotating cam 24 which is also carried by the web of brake shoe l0 and constitutes a positioning means for the pivoting lever 16. To this effect, the shaft of cam 24 (not shown) projects through an opening in the backing plate of the brake an is so shaped as to be easily operable from the outside with an appropriate tool such as, for instance, a screwdriver, Thus the cam 24 can be rotated between two end positions both determined by the abutting engagement of the eccentric pin 22 with the bottom portion of slot 20. Between these end positions, the rotation of cam 24 causes the pin 22 to slidably engage the sides of slot 20 to pivot the lever 16 between two distinct angular positions; and the location of the respective centers of rotation as well as the general dimensions of the mechanism can be easily determined in such a manner that one of said angular positions (shown in dotted lines on FIG. 2) corresponds to the un stressed condition of spring 14 whereas the other one (shown in solid lines) corresponds to the stressed condition thereof. Furthermore, the mechanism will be advantageously designed so that this last-mentioned angular position of lever 16 be reached for a displacement of the rotating cam 24 slightly beyond that position which causes spring 14 to get its greatest elongation, that is to say the position where the radius joining the axis of cam 24 to that of pin 22 becomes perpendicular to the lateral edges of slot 20. This feature results in the eccentric pin 22 being urged by spring 14 itself into abutting engagement with the bottom portion of slot 20, thus exerting a selflocking effect with respect to the lever 16 for holding same in its operative angular position.

The above described mechanism operates as follows:

When assembling the brake, the shoes are first properly located on the backing plate with their pivoting lever or levers 16 in their inoperative position as shown in dotted lines on FlG. 2. The return spring 14 can thus be hooked between the shoe 12 and the end of lever 16 on shoe 10 without difficulty since being in an unstressed condition. Then the cam 24 will be rotated from the outside of the brake with a convenient tool in the direction of arrow A. This will cause the lever 16 to be progressively pivoted toward the left while simultaneously stressing the spring 14 until the latter reaches its greatest elongation, after what further rotation of the cam 24 will cause the eccentric pin 22 to be urged against the bottom portion of slot 20. The lever 16 will thus be held, as explained above, in its operative angular position shown in solid lines on FIG. 2. The preceding steps will, of course, have to be performed in a converse order for dismounting the brake.

The above described mechanism may be modified in many ways, for instance by providing each brake shoe with one or more pivoting levers, or by modifying the respective locations of the pivoting centers and hooking points, or by still replacing the rotating cam with any suitable equivalent means, and it should be understood that all of these modified embodiments are included in the scope of protection as defined by the following claims:

1 claim:

1. In a drum brake:

a pair of brake shoes;

a return spring interconnecting said shoes;

a lever pivotally mounted on one of said shoes extending generally transversely to the axis of the spring;

one end of said lever having a hooked portion;

one end of said return spring being attached to said hooked portion;

said lever pivoting between a first position in which the spring is relatively relaxed to a second position in which the spring is stressed to exert a force on the shoes;

positioning means for pivoting said lever; and

said positioning means including a slot in said lever, and a rotating cam member carried by said one shoe and having an eccentric member slidably received in the slot in said lever whereby rotation of the cam member pivots the lever between said first and second positions.

position.

4. The invention of claim 1, wherein said cam member extends through the brake whereby the cam member may be rotated from the exterior of the brake by use of an appropriate 5 tool. 

1. In a drum brake: a pair of brake shoes; a return spring interconnecting said shoes; a lever pivotally mounted on one of said shoes extending generally transversely to the axis of the spring; one end of said lever having a hooked portion; one end of said return spring being attached to said hooked portion; said lever pivoting between a first position in which the spring is relatively relaxed to a second position in which the spring is stressed to exert a force on the shoes; positioning means for pivoting said lever; and said positioning means including a slot in said lever, and a rotating cam member carried by said one shoe and having an eccentric member slidably received in the slot in said lever whereby rotation of the cam member pivots the lever between said first and second positions.
 2. The invention of claim 1, wherein one of said first or second positions of the lever is determined by the engagement of said eccentric member with the bottom portion of said slot.
 3. The invention of claim 2, wherein said lever is locked in position by rotation of the cam through an arc greater than that required to move the lever from the first to the second position.
 4. The invention of claim 1, wherein said cam member extends through the brake whereby the cam member may be rotated from the exterior of the brake by use of an appropriate tool. 